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我有一个表单，它在提交时会将输入的数据输出到表单中，并将其输出到查询结果中。如果文本框为空，它将搜索该特定字段的所有数据。目前我的查询输出：查询输出比它应该做的更多的行，这是为什么？
SessionId ModuleId CourseId ClassId StudentUsername TeacherUsername Grade
ABB CHT2520 INFO101 104 u0867587 m.prigmore A
ABB CHI2550 INFO101 101 u0867587 j.lu A
ABB CHI2550 INFO101 104 u1231231 j.lu F
ABB CHT2520 INFO101 101 u1231231 m.prigmore F
NVK CHI2550 INFO101 101 u0867587 j.lu F
RMI CHI2565 INFO101 102 u0660663 j.forden F
它正在输出更多的行，然后它应该这样做。一个学生属于同一个班级的一个单元。问题在于它显示一个学生属于两个班级，因为一个模块不正确。它这样做的原因是因为它根据学生正在学习的模块来识别学生所在的班级。
因此，如果模块'CHI2550'有两个班级，任何需要模块'CHI2550'的学生被分配到两个班级，但应该是一个班级的学生被分配到一个班级，并且应该由'StudentClass'表。问题是，如果我在其中一个JOINS中包含'StudentClass'，则查询输出9行。
查询应的输出这样的：
SessionId ModuleId CourseId ClassId StudentUsername TeacherUsername Grade
ABB CHI2550 INFO101 101 u0867587 j.lu A
ABB CHI2550 INFO101 104 u1231231 j.lu F
NVK CHT2520 INFO101 103 u0867587 m.prigmore F
RMI CHI2565 INFO101 102 u0660663 j.forden F
我怎样才能得到查询到输出上面的结果呢？下面是查询：
下面是每个表和它们的数据（因为我所面临的问题，最重要的表是StudentClass，班，学生，模块）：
Course Table:
CourseId CourseName Duration
INFO101 Bsc Information Communication Technology (ICT) 3/4
CourseModule Table:
CourseId ModuleId
INFO101 CHI2550
INFO101 CHI2565
INFO101 CHT2520
Module Table:
ModuleId ModuleName Credits
CHT2520 Advanced Web Programming 20
CHI2565 E-Commerce Business and Technology 20
CHI2550 Modern Database Applications 20
Session Table:
SessionId ModuleId Semester SessionDate SessionTime TeacherId Room Building
NVQ CHT2520 Spring 2011-03-21 13:00:00 T2 CW2/04 Canalside West
NVK CHT2520 Fall 2011-11-10 10:00:00 T2 CW2/04 Canalside West
RMI CHI2565 Fall 2011-09-13 12:00:00 T5 CW5/01 Canalside West
RMT CHI2565 Spring 2011-03-29 14:00:00 T2 CW2/04 Canalside West
ABB CHI2550 Spring 2011-03-15 12:00:00 T1 CW4/10 Canalside West
ABH CHI2550 Summer 2011-05-03 15:00:00 T4 CW4/10 Canalside West
Grade_Report Table:
StudentId SessionId Grade Mark
S1 NVK F 5
S2 ABB A 80
S1 ABB A 80
S3 RMI F 0
Student Table:
StudentId StudentForename StudentSurname Year StudentUsername CourseId
S1 Mayur Patel 3 u0867587 INFO101
S2 Jim Carlton 3 u1231231 INFO101
S3 Ahmed Seedat 3 u0660663 INFO101
S4 Amar Barot 3 u0954857 INFO101
S5 Richard Davies 3 u0877223 INFO101
StudentClass Table:
ClassId StudentId
101 S1
102 S3
103 S1
104 S2
Class Table:
ClassId Room ClassDay ClassTime ModuleId CourseId TeacherId
101 CW4/10 Thursday 10:00:00 CHI2550 INFO101 T1
102 CW5/01 Wednesday 12:00:00 CHI2565 INFO101 T5
103 CW2/04 Monday 15:00:00 CHT2520 INFO101 T2
104 CW4/10 Thursday 11:00:00 CHI2550 INFO101 T1
Teacher Table:
TeacherId TeacherForename TeacherSurname TeacherUsername TeacherPassword
T1 Joan Lu j.lu scomp21
T2 Martyn Prigmore m.prigmore prigmore36
T3 Arshard Ali a.ali aliict
T4 Paul Judge p.judge data01
T5 John Forden j.forden hudds_10